what causes my vehicle to start up and then automatically shut off?

What is your question?

when i start my 2002 isuzu axiom, the rpms raise to about 3 and then they go below 1 and then the vehicle shuts off. it will be driving fine and then i have to stop at a stop sign and it will cut off on me. it is the first time for doing this and it just seems to happen when the vehicle sits over long periods of time, such as over night. lately i can not get it to stay running. any help or ideas